


When the Need Arises

by Larkspur_Productions



Category: Undertale (Video Game)
Genre: Alternate Universe - Swapfell, Alternate Universe - Underswap, Bloodplay, Breastfeeding, Dubious Consent, Dubious Science, Ecto-Boobs (Undertale), Ecto-Tongue (Undertale), Implied/Referenced Rape/Non-con, M/M, Nanny Blue, Science Kink, Swapfell Sans, Underswap Sans, ecto-blood, nanny kink, science rotten, science sans
Language: English
Status: Completed
Published: 2016-09-13
Updated: 2016-09-13
Packaged: 2018-08-14 20:48:27
Rating: Mature
Warnings: Rape/Non-Con
Chapters: 1
Words: 1,465
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/8028418
Author URL: https://archiveofourown.org/users/Larkspur_Productions/pseuds/Larkspur_Productions
Summary: A fanfic based on an au version of an au where swapfell sans (Rotten) is a scientist in charge of a lab where underswap sans (Blue) works as a nanny to a group of mentally unstable monsters. Sorta part of a series that me and sigiseraphina have been talking about for a while now.





	When the Need Arises

**Author's Note:**

  * For [sigiseraphina](https://archiveofourown.org/users/sigiseraphina/gifts).



> When Blue finds himself asking the boss for yet another favor the boss takes this as a time fore some fun. All things come with a price after all.

It had only been a month since the incident, and when the poor fox monster learned that she now carried a child she didn't ask for it was surprising when the girl wrapped herself protectively over her stomach and begged to keep the child. Blue had been the one to help her keep it as he begged the boss not to get rid of the souling. It was nothing short of a miracle when the doctor gave the okay.

A week after Blue again came in and asked for a small favor, let her have maternity leave, don't test on her while she has the child. Last time was a miracle but this time Blue had to work for it as he assisted the doctor with his ever growing stacks of paperwork for the rest of the month.

At the end of the month however Blue began to notice something worrying. The cell that the lab rat was kept in was far to small for both monsters. the crib alone took up half of the area. Blue had taken a deep breath and marched to the boss's office where he straightened up his outfit, stood up straight and thought of the perfect speech to give as he knocked on the door.

"Come in" Came the doctor's voice, it was almost calm. Good, thought Blue, better he be happy than be angry, and he opened the door and stepped in.

"Sir? I know you've done a lot already for Bunny by letting her keep her child a-and not testing on her but I was wondering if maybe you could give her someplace bigger to sleep? That cell is really small and a growing a baby n-needs room to-"  
"Entertain me."  
"wh-what?"  
"I said, entertain me. If it's so important to you I expect to be entertained. so, entertain me Mr. Aster."

Blue gulped slightly and nodded with a "yes sir" as he quickly tried to think of something, anything to entertain the strict doctor. Thinking back he remembered the way the doctor always seemed to be fascinated by his ecto-boobs, perhaps, no. He quickly pushed the thought out of his might, the doctor wouldn't want anything to do with something so lewd, he was a professional.

"I'm waiting Mr. Aster." The doctor growled out, causing Blue to jump slightly.

"I-is there anything you would want for me to do? uh I...could juggle?" Blue asked hoping for something somewhat easy as a nervous smile crossed his face. The doctor didn't seem to even entertain the thought as he scuffed and crossed his arms. "Do you think I'm a child? You had better think of something soon or I won't even consider giving the rat a room."

Blue frowned and looked at his shoes as he thought. Singing? No. Maybe talk about his research? He must be bored of that. Blue clenched his hands into fists as he desperately tried to think of something.

"Mr. Aster if I was a lab rat how would you treat me?" The doctors words made Blue look up with confusion as his thoughts flew away. 

"Excuse me? what do you mean sir?" If the doctor was one of the lab rats? what strange question to ask at this time.

"I mean what I said. If I was a lab rat. If you were to care for me. How would you do it?" The doctor leaned forward in his chair slightly with a smirk, awaiting Blue's answer.

"Well that depends. all of them are different and need different care and-"  
"-and how would you take care of me?"

Blue must be imagining things when he saw the doctor lick his teeth slowly as he stared at Blue. Was he looking at his chest? No. He's a professional. Even when Blue had to start sucking him off it was for a scientific reason. Blue sighed as he thought about the question.

"W-well um... you seem to have a bit of OCD and um you enjoy puzzles...s-so maybe a Rubix cube to keep you busy, or maybe-"  
"what if I don't want that...nanny?"

Blue was shocked. He was fairly used to being called that by the lab rats but the way the doctor seemed to almost moan out the word, it brought a dark blush to Blue's cheeks.

"W-well there are other things I could try-"  
"What happens if I'm bad?"  
"Wha-? I...well then you'd be punished."  
"How?"  
"That d-depends... uh I usually go with spanking but for some-"  
"What if I'm good?"  
"W-well you'd get a reward...a treat."  
"What kind?"  
"Well sometimes I cuddle them o-or-"  
"I like milk"

Did Doctor just say that? Oh yes, now it was clear how the doctor was staring at Blue's chest with hunger as he slowly leaned forward. Blue couldn't believe what he was witnessing. Was the doctor really asking for Blue to....

"do you want milk, sir?" Blue whispered slightly as he already felt the magic get ready. The doctor's smile confirmed Blue's suspicion as Rotten leaned back with a smirk. "yes nanny."

Blue gulped as his blush grew brighter before he took a deep breath, reminding himself that this was all for a very good reason. Slowly Blue let his ecto-breasts form, pushing against top of the outfit he was wearing. The doctor nearly jumped out of his seat at the sight of them, wanting to squeeze and fondle and suck on them till Blue was crying, but he didn't and remained seated as he watched the show. Once Blue's breasts were formed he looked at the doctor nervously.

"I-is this what-"  
"yes now come here."

Blue took yet another deep breath as he walked around the doctor's desk just as Rotten turned in his seat and patted his lap. "face me." Rotten commanded, his eyes never really moving from his treat. Blue nodded silently at the command before pulling himself into the doctor's lap with his knees tucked to the side of Rotten's legs. The doctor smiled as he reached behind Blue and carefully untied a ribbon that allowed the top of the outfit become slack, before pulling the rest of it down, leaving Blue half naked.

The doctor didn't seem to waste much time as he reached up and squeezed Blue's breasts as hard as he could as if he was using them to release his stress. Blue let out a gasp and a whine as some of the doctor's sharpened claws dug into his soft ecto-flesh. Rotten didn't pay any attention to the sounds Blue was making as he started to massage and squeeze the ecto-boobs with fascination.

Soon the doctor leaned forward and dragged his tongue against Blue's nipple as a purr rolled out of his chest. Blue gasped and bit his tongue as the doctor lapped at his chest. He had no idea that the doctor had a tongue ring, and it was driving Blue up the wall. However soon the licking was ceased as the doctor finally latched on and began to suckle. His hands pressing against each breast slowly and needy. It didn't take long for Blue to start to lactate and as warm milk filled his mouth the doctor gulped and moaned as his suckling grew despite for more. Blue tried hard to hold back the sounds he was making. it wasn't exactly the suckling that was making this hard, he was far too used to that, but it was the way the doctor would drag his tongue ring in circles around his nipple, it was the way the other kneaded into Blue's chest with claws that drew prickles of liquid magic. Luckily Blue was spared from an embarrassing moan as the doctor finally pulled away, having got his fill.

"Alright, she can have a spare room." The doctor said almost casually as he lapped up a few drops of milk that were dripping out of Blue's nipple. Finally he wiped of his mouth and gulped down any remaining drops in his mouth. Blue was slightly stunned at the doctors words but quickly realized that he had better get off of Rotten before he changed his mind.

"Thank you Dr. Rotten. thank you so much." Blue said as he fixed his outfit. The doctor smiled slightly at the thanks as he leaned back in his chair. "You are welcome Mr. Aster. If you need anything else. You know what to do."

Blue stopped and blushed as he thought of what the doctor meant but as quickly as it came it was soon pushed aside as Blue checked his watch and gasped. "I have to go! thank you again Dr. Rotten!" Blue called out as he quickly left.

Dr. Rotten stared at the door after Blue left and slowly smiled.

"You're welcome, Blue."


End file.
